{
  "bibcode": "2021GCN.30483....1P",
  "body": "K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), P.A. Evans (U.\nLeicester), M.G. Bernardini (INAF-OAB), E. Ambrosi  (INAF-IASFPA) , M.\nCapalbi (INAF-IASFPA), J. D. Gropp (PSU), J.A. Kennea (PSU), A.\nTohuvavohu (U. Toronto) and P. D'Avanzo report on behalf of the\nSwift-XRT team:\n\nWe have analysed 6.3 ks of XRT data for GRB 210722A (D'Avanzo et al.\nGCN Circ. 30475), from 91 s to 47.1 ks after the  BAT trigger. The data\ncomprise 294 s in Windowed Timing (WT) mode with the remainder in\nPhoton Counting (PC) mode. Using 3301 s of PC mode data and 8 UVOT\nimages, we find an enhanced XRT position (using the XRT-UVOT alignment\nand matching UVOT field sources to the USNO-B1 catalogue): RA, Dec =\n27.03023, -6.34758 which is equivalent to:\n\nRA (J2000): 01h 48m 07.26s\nDec(J2000): -06d 20' 51.3\"\n\nwith an uncertainty of 2.0 arcsec (radius, 90% confidence).\n\nThe late-time light curve (from T0+4.5 ks) can be modelled with a\npower-law decay with a decay index of alpha=1.31 (+0.10, -0.09).\n\nA spectrum formed from the WT mode data can be fitted with an absorbed\npower-law with a photon spectral index\tof 2.20 (+/-0.05). The\nbest-fitting absorption column is  4.2 (+1.0, -0.9) x 10^20 cm^-2, in\nexcess of the Galactic value of 2.2 x 10^20 cm^-2 (Willingale et al.\n2013). The PC mode spectrum has a photon index of 1.84 (+0.11, -0.10)\nand a best-fitting absorption column of 3.5 (+2.4, -1.2) x 10^20 cm^-2.\nThe counts to observed (unabsorbed) 0.3-10 keV flux conversion factor\ndeduced from this spectrum  is 3.5 x 10^-11 (3.8 x 10^-11) erg cm^-2\ncount^-1. \n\nA summary of the PC-mode spectrum is thus:\nTotal column:\t     3.5 (+2.4, -1.2) x 10^20 cm^-2\nGalactic foreground: 2.2 x 10^20 cm^-2\nExcess significance: <1.6 sigma\nPhoton index:\t     1.84 (+0.11, -0.10)\n\nIf the light curve continues to decay with a power-law decay index of\n1.31, the count rate at T+24 hours will be 0.013 count s^-1,\ncorresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.4 x\n10^-13 (4.8 x 10^-13) erg cm^-2 s^-1.\n\nThe results of the XRT-team automatic analysis are available at\nhttp://www.swift.ac.uk/xrt_products/01061223.\n\nThis circular is an official product of the Swift-XRT team.",
  "circularId": 30483,
  "createdOn": 1627050438000,
  "email": "pae9@leicester.ac.uk",
  "subject": "GRB 210722A: Swift-XRT refined Analysis",
  "submitter": "Phil Evans at U of Leicester  <pae9@leicester.ac.uk>",
  "eventId": "GRB 210722A"
}